Updated the cx16 library to the Commander X16 Kernal's prerelease 35.

libsrc/cx16/waitvsync.s

@@ -1,9 +1,10 @@
 ;
-; 2019-09-26, Greg King
+; 2019-12-23, Greg King
 ;
 ; void waitvsync (void);
+; /* Wait for the start of the next video field. */
 ;
-; VERA's vertical sync causes IRQs which increment the jiffy clock.
+; VERA's vertical sync causes IRQs which increment the jiffy timer.
 ;
 
         .export         _waitvsync
@@ -11,7 +12,10 @@
         .include        "cx16.inc"
 
 _waitvsync:
-        lda     TIME + 2
-:       cmp     TIME + 2
+        ldx     VIA1::PRA2      ; (TIMER is in RAM bank 0)
+        stz     VIA1::PRA2
+        lda     TIMER + 2
+:       cmp     TIMER + 2
         beq     :-              ; Wait for next jiffy
+        stx     VIA1::PRA2
         rts